Has anybody seen/heard/tried this:http://www.futurlec.com/Flow_Sensor.shtml
(next to last item on page)
If it works, it is a good price ($18.90) for a sensor with a build-in flow rate readout. No switching for auto shutdown, but at least we could see the flow rate.
(I have ordered from this company before - think they are in China and it takes a couple of weeks to get product here, but they seemed reliable and honest when I ordered from the in the past.)